A web service allows applications to communicate over a network through standards-based web protocols. There are two main types of web services: SOAP and RESTful. SOAP uses XML messages with a defined envelope, header, and body structure. The SOAP envelope provides packaging for the message and ensures the receiver knows when the full message is received. RESTful web services use HTTP requests to access and use web resources through a uniform and predefined set of stateless operations.

2. Web Service
• A Web Service can be defined by following ways:
– is a client server application or application component
for communication.
– method of communication between two devices over
network.
– is a software system for interoperable machine to
machine communication.
– is a collection of standards or protocols for exchanging
information between two devices or application.

3. • As shown in the figure, java, .net or PHP applications can
communicate with other applications through web service
over the network.
• For example, a Java application can interact with Java, .Net
and PHP applications. So web service is a language
independent way of communication.

4. Types of Web Services
• There are mainly two types of web services.
– SOAP web services.
– RESTful web services.

5. SOAP
• SOAP is an acronym for Simple Object Access
Protocol. It is an XML-based messaging
protocol for exchanging information among
computers.
• SOAP is an application of the XML
specification.

6. SOAP - Message Structure
• A SOAP message is an ordinary XML document
containing the following elements −
– Envelope: Defines the start and the end of the
message. It is a mandatory element.
– Header: Contains any optional attributes of the
message used in processing the message, either at an
intermediary point or at the ultimate end-point. It is
an optional element.
– Body: Contains the XML data comprising the message
being sent. It is a mandatory element.
– Fault: An optional Fault element that provides
information about errors that occur while processing
the message.

7. • All these elements are declared in the default
namespace for the SOAP envelope
− http://www.w3.org/2001/12/soap-
envelope
• The default namespace for SOAP encoding
and data types is
− http://www.w3.org/2001/12/soap-encoding

8. SOAP - Envelope
• The SOAP envelope indicates the start and the
end of the message so that the receiver knows
when an entire message has been received.
• The SOAP envelope solves the problem of
knowing when you are done receiving a
message and are ready to process it.
• The SOAP envelope is, therefore, basically a
packaging mechanism.

9. • Every SOAP message has a root Envelope
element.
• Envelope is a mandatory part of SOAP message.
• Every Envelope element must contain exactly one
Body element.
• If an Envelope contains a Header element, it must
contain no more than one, and it must appear as
the first child of the Envelope, before the Body.
• The envelope changes when SOAP versions
change.
• The SOAP envelope is specified using
the ENV namespace prefix and the Envelope
element.

10. • The optional SOAP encoding is also specified
using a namespace name and the
optional encodingStyle element, which could
also point to an encoding style other than the
SOAP one.
• A v1.1-compliant SOAP processor generates a
fault upon receiving a message containing the
v1.2 envelope namespace.
• A v1.2-compliant SOAP processor generates
a VersionMismatch fault if it receives a
message that does not include the v1.2
envelope namespace.